1. Field of the Invention
This invention pertains to coating processes and coated products, and more particularly to production of epoxy coated, corroded metal surfaces.
2. Description of the Prior Art
Corroded metal surfaces contain deteriorated paint particles and oxidation products of the metal substrates. The painting of these corroded surfaces requires the coating composition to penetrate and bind the loose corrosion products and to adhere firmly to the underlying substrate. Coating compositions containing alkyds or drying oils provide relatively superior adhesion to such corroded surfaces. However, the durability of such coating compositions is considerably shorter than high performance coating compositions containing epoxy or vinyl resins. The epoxy and vinyl systems, while providing excellent weathering, require very clean surfaces in order to achieve the requisite adhesion. The requisite surface preparation, through such cleaning procedures as sand blasting, accounts for a major portion of the costs incurred during painting operations. Furthermore, the silicosis hazard associated with the use of sand and grit requires precautionary measures to be taken to minimize worker exposure and environmental pollution. These measures further add to the cost of surface preparation and in some instances prevent its use.
There is therefore a need for coating compositions which when applied to minimally cleaned, corroded metal surfaces provide wetting properties, as well as sufficient adhesion, to yield good protective action of the surfaces, without the need for intensive surface preparation.
Various polyepoxide coating compositions containing polyamines have been described as having general coating utility or as useful in a variety of specific applications.
U.S. Pat. No. 3,316,185 (Reinking) discloses curable polyepoxide coating compositions comprising a mixture of a polyepoxide having an epoxy equivalency of greater than 1 and a liquid glycol diamine. U.S. Pat. No. 3,380,881 (Williamson et al.) describes a curable composition comprising polyepoxide and glycol polyamine components useful to bond implosion shields to curved surfaces of television picture tubes. U.S. Pat. No. 3,496,138 (Sellers et al.) discloses adducts of polyglycol diamines and curable compositions comprising polyepoxides and such adducts, useful for coating a variety of surfaces. U.S. Pat. No. 3,257,342 (Kwong) describes curable epoxy compositions containing polyamino polyamides of diaminopolyethers and dicarboxylic acids useful for electrical insulation. U.S. Pat. No. 3,645,969 (Harvey) discloses curable polyepoxide compositions containing a mixture of polyglycol polyamine and an alkylene polyamine as curing agent, useful in coating, casting or filament winding applications. U.S. Pat. No. 4,352,920 (Kluger) discloses epoxy resin compositions containing aminoalkoxy curing agents useful in structural applications and in protective coatings. U.S. Pat. No. 4,421,906 (Waddill et al.) discloses water-based epoxy resin coating compositions containing bisphenol A type epoxy resins, modified by partial reaction with polyoxylalkyleneamines, combined with an aqueous solution of an amidopolyamine.